The field of the invention is in the art of electronic measurement of small distances, and particularly in the art of measuring the clearances of the tips of turbomachine blades.
Knowledge of the tip clearance existing during actual operation of a turbomachine is vitally important both from the standpoint of mechanical integrity and also for the thermodynamic performance of the machine. It has previously been measured with eddycurrent devices, by capacitance probes, and more recently by optical means. However, all of these systems have depended upon an analog signal subject to one or more forms of considerable error. The following patents may be of value in adding to the background of the invention; U.S. Pat. No. 3,614,617 to patentee Blake; U.S. Pat. No. 3,856,410 to patentee Swift and U.S. Pat. No. 3,908,444 to patentee Peter.